The research project will focus on the structure and regulation of the gene encoding tryptophan hydroxylase (TPH), the rate-limiting enzyme in the synthesis of serotonin. While TPH is known to be regulated through protein kinase-mediated phosphorylation, this key enzyme may also be regulated at the level of gene expression. Using oligonucleotide probes based on cloned, pineal cDNAs encoding TPH, we can detect mRNA from the CNS. We have shown that the CNS mRNA is altered at the 5' end when compared with the cloned, pineal cDNAs. Furthermore, we have shown that pharmacological agents which alter serontonin levels alter steady-state TPH mRNA levels. We now propose to obtain genomic- and CNS-specific cDNA- clones specific for TPH and to study the mechanism of gene regulation. Lastly, we will study the potential involvement of receptor events in the regulation of TPH mRNA levels.